raised air intake shouldnt cause it,worth checking pipes arent collapsing on suction side of turbo and split on pressure side ,sluggishness can be caused by a few things and its wise to start of with well serviced engine before trying to fix it ie filters ,tappets ,timing ,slackening front banjo to see if copious air free fuel is reaching pump (fitting a clear plastic pipe between filter and front banjo is a useful addition to be able to see fuel ) fuel pump can be put to its best by fitting a 9.5 drill bit fully into pump through pulley then slackening the 3 bolts and holding center nut clockwise against the pin then retighten the 3 bolts ,try engine ,you can then repeat using smaller drill bit 9 then 8.5 then 8 etc till diesel knock becomes apparent then go back one larger drill size till knock goes thats optimum pump timing and can be quite noticeable in performance